The present invention relates generally to spring suspensions for off-road vehicles such as earthmoving machines.
In the past it has been the practice to simply dispense with springing of the chassis in an off-road vehicle such as an earthmoving scraper. This has resulted in a rough ride for the operator and the transmission of destructive shocks to the vehicle when negotiating rough ground. In those instances where springing has been employed, particularly for earthmoving vehicles of light construction, the tendency has been to utilize the principles of suspension which have been used in automobiles and highway trucks, that is, each wheel has been provided with individual springing and damping means. The individual springing has meant that irregularities in ground contour causing momentary tilting to right or left must be accommodated by opposite movements in the right and left suspension means. This causes constant and unnecessary exercising in the suspensions on rough terrain with generation of high suspension forces resulting in aggravated wear and high maintenance cost. Moreover, where the wheels are separately sprung with the desired softness or compliance there is a sacrifice in roll stability, that is, there is lowered resistance to sway or roll between suspensions at one axle location. As a result, where separate springing is used, it is often necessary to compromise springing, roll stability, or both in order to achieve a practical solution.
Some efforts have been made in the past to depart from individual wheel springing as practiced, for example, in an off-road truck of early Dart manufacture. In such structure a single horizontal pinned joint was provided between the axle housing and the lower end of the suspension to permit oscillation of the axle housing in a plane transverse to the center line of the vehicle. Such an arrangement, however, subjected the suspension device to rather large side forces and resulted in a coupling of motion in both the transverse and longitudinal directions, in addition to the vertical loads required of the suspension. Such side forces and couples are aggravated further by use of oscillation limit stops requiring the suspension to support the entire axle load at a wheel at one end of the axle. A suspension of adequate capability constructed on this order utilizes space down the chassis center line which is often needed for components such as engine and power train. In addition to interfering with critical components in some vehicle arrangements, the suspension is of inherently increased size and cost. Moreover, no "roll stability" is provided about the longitudinal oscillation axis.
Finally, in the so-called "cushion hitch" used in certain Caterpillar earthmoving vehicles the axle is rigidly attached to the frame or chassis which is connected to the tractor by a joint which permits relative rolling movement about a longitudinal oscillation axis. The only cushioning against bumps and irregularities is that which occurs in the tires and the only springing is that which is provided between the two main portions of the vehicle i.e., between the front or tractor section and the rest of the vehicle. Moreover, there is no control of "roll stability" about the longitudinal oscillation axis.